The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
A toothache is a pain in or around a tooth that may be caused by: Tooth decay; Abscessed tooth; Tooth fracture; A damaged filling; Repetitive motions, such as chewing gum or grinding teeth; Infected gums; Symptoms of a toothache may include: Tooth pain that may be sharp, throbbing, or constant. In some people, pain results only when pressure is applied to the tooth. Swelling around the tooth; Fever or headache; Foul-tasting drainage from the infected tooth; When Should I See a Dentist About a Toothache? See your dentist as soon as possible about your toothache if: You have a toothache that lasts longer than 1 or 2 days; Your toothache is severe